The present invention relates to a magnetic-field-sensitive component comprising at least one diluted magnetic semiconductor, to a magnetic field sensor device and to a memory structure, each incorporating this component, and to a method of detecting a magnetic field by means of this component.
Magnetic field sensors are used in many devices, such as magnetometers, compasses, angle sensors, sensitive elements of hard disk read heads or magnetic tape readers. Various principles are used, but for most applications, such as for magnetic hard disk read heads, it is desired to obtain a higher sensitivity to low-intensity magnetic fields and/or to very localized magnetic fields.
At the present time, it is common practice to use, as magnetic field sensors, Hall-effect probes and magnetoresistive sensors (exhibiting anisotropic or giant magnetoresistance). The latter sensors are used in particular in modern hard disk read heads, where they advantageously replaced inductive read heads owing to their greater sensitivity to low-intensity magnetic fields.
Nevertheless, these magnetoresistive sensors have the drawback of being limited to a narrow range of magnetic field intensities for obtaining a high sensitivity, before the magnetization of the active layer, which is generally chosen from a soft material, saturates.
It is also known to use inductive sensors that do not have this limitation in terms of accessible field range but which can be used only for detecting variations in a magnetic field, and not the intensity of a static magnetic field.
More recently, to meet ever greater sensitivity requirements, it has been sought to develop magnetic field sensors based on tunnel magnetoresistance in order to constitute the sensitive element of hard disk read heads. However, it is predictable that the reduction in size of the magnetic bits supporting the information on hard disks, and therefore the reduction in the radiated magnetic field that can be detected by the read element, will require the search for novel sensors that are even more sensitive to these small magnetic fields.
A. D. Kent et al., J. Appl. Phys., 76, 6656 (1994) proposed in this article a novel concept of magnetic field sensor, based on measuring the Hall effect in a two-dimensional gas of charge carriers (electrons or holes) within a thin semiconductor film. In such systems, such as a thin film of a GaAs semiconductor between two AlGaAs films, the measured Hall voltage is higher the lower the carrier concentration.
Mention may also be made of the work carried out by F. Takano et al., Physica E, 12, 370 (2002) which are placed under particular conditions of a low concentration of magnetic elements and carried out at low temperature, in order to observe the quantum Hall effect in a magnetic well of a diluted CdMnTe magnetic semiconductor. It should be noted that, under these conditions, quantum Hall effect plateau response as a function of the applied magnetic field has resulted in magnetic field intensity ranges in which no variation of the Hall voltage can be detected.
A major drawback of the devices described in these documents is that they are unable to detect magnetic fields having a very low intensity and/or are highly localized in space.
Even more recently, document U.S. Pat. No. 6,910,382 has presented a magnetic field detection device, in particular for hard disk read heads, which is based on the giant planar Hall effect in diluted magnetic semiconductors. More precisely, this device is designed to detect changes in the properties of domain walls, such as changes in orientation of magnetization domains.
It should be noted that the device described in the above document is not designed to measure magnetic field intensities, but only changes in magnetic properties.